I should have known you people would have a longer-winded name for it; I'll be more cautious next time I think there's no difference between British names and American names for the same thing. I should have looked at this first:

‘In the United States and Canada, a residual current device is also known as a ground fault circuit interrupter (GFCI), ground fault interrupter (GFI) or an appliance leakage current interrupter (ALCI). In Australia they are sometimes known as "safety switches" or simply "RCD".’